1. Field of the Invention
The present invention relates to a method of fabricating a liquid crystal display substrate for use in a liquid crystal display device and a liquid crystal display substrate which is made by this method of fabrication.
2. Description of the Related Art
Conventionally, a liquid crystal display substrate, which is a display member of a liquid crystal display device, is constituted by superimposing two sheets of transparent glass substrates each other, which are different in size, via a seal agent.
FIG. 1A is a perspective view showing a constitution of a conventional liquid crystal display substrate, and FIG. 1B is a sectional view taken on the line Z-Z′ of FIG. 1A. As shown in FIGS. 1A and 1B, a conventional liquid crystal display substrate 1 is constituted by superimposing a first substrate 11 and a second substrate 12 disposed as opposed to this first substrate 11 and having a CF (color filter: not shown) via a seal layer 2 and a liquid crystal layer 20. The seal layer 2 is sandwiched between the first substrate 11 and the second substrate 12. Moreover, when superimposing the second substrate 12 over the first substrate 11, in an area where the first substrate 11 is projecting (hereinafter, referred to as extra length portion 3), a terminal portion 31 having a drive circuit (not shown) consisted of a thin film transistor and the like is formed. The seal layer 2 is formed along a circumferential portion of a face on which the first substrate 11 and the second substrate 12 oppose to each other, within a space formed by the seal layer 2, the first substrate 11 and the second substrate 12 (hereinafter, referred to as liquid crystal enclosing portion), a liquid crystal agent is enclosed, and a liquid crystal layer 20 is formed. The liquid crystal layer 20 and the seal layer 2 can be seen through the second substrate 12 in FIG. 1A. In addition, as shown in FIG. 1B, in a conventional liquid crystal display substrate 1, a terminal face 2a of the seal layer 2 forms a concave portion relative to a terminal face 11a of the first substrate 11 and a terminal face 12a of the second substrate 12.
Next, a conventional method of fabricating the liquid crystal display substrate 1 will be described below. FIG. 2A to FIG. 2F are perspective views showing a procedure of a method of fabricating the conventional liquid crystal display substrate 1. As shown in FIG. 2A, first, a seal agent is applied using a dispenser 14 and the like on an adhesive surface of the first substrate 11 consisted of glass, and on the first substrate 11, the seal layer 2 is formed. At this moment, the seal layer 2 is formed so as to enclose a space in which a liquid crystal agent is enclosed in a later procedure, that is to say, a liquid crystal enclosing portion. This liquid crystal enclosing portion is enclosed with and formed by the seal layer 2, the first substrate 11 and the second substrate 12, which is superimposed over the first substrate 11 in a later procedure. Moreover, in the seal layer 2, opening portion 4, by which the liquid crystal enclosing portion is connected to the external is formed in order to inject a liquid crystal agent from the external into the liquid crystal enclosing portion.
On the other hand, as shown in FIG. 2B, a spacer 16 is scattered by a scattering nozzle 15 on the adhesive surface of the second substrate 12 consisted of glass. It should be noted that the adhesive surface of the first substrate 11 and the adhesive surface of the second substrate 12 refer to faces opposed to each other when each substrate is superimposed.
Next, as shown in FIG. 2C, a superimposed substrate 13 is formed by superimposing the first substrate 11 and the second substrate 12 so that the adhesive surface of the first substrate 11 and the adhesive surface of the second substrate 12 oppose to each other via the seal layer 2.
Subsequently, as shown in 2D, on the surface and back of the superimposed substrate 13, a flaw (scribe crack 18) is formed by a cutter 17 and the like. This scribe crack 18 is formed in order to cut the first substrate 11 and the second substrate 12 in desired dimensions. Dimensions are set, for example, so as to provide the extra length portion 3 (see FIG. 1) by setting the dimensions of the first substrate 11 larger than that of the second substrate 12 to have the terminal portion 31.
Subsequently, as shown in FIG. 2E, the superimposed substrate 13 is turned upside down, a break bar 19 and the like impact on a substrate (the first substrate 11) separate from the substrate (the second substrate 12) on which the predetermined scribe crack 18 is formed, thereby cracking (breaking) the substrate from the scribe crack 18 as the starting point.
The liquid crystal display substrate 1 as shown in FIG. 2F is tailored by repeating these breaks.
However, there are the following problems shown below in a conventional liquid crystal display substrate and its method of fabrication.
First, in a cutting process (hereinafter, referred to as mechanical cutting process) of the superimposed substrate 13 performed by the break bar 19, its cutting surface may be roughed, as a result, cutting chips of glass such as cullet and particle may be attached on the cutting surface. Therefore, in order to remove glass chips such as cullet and particle from the product, it is required to provide abrasive machining process and washing process of the substrate after the mechanical cutting process, thereby resulting in problems of complication of fabrication processes and an increase of fabrication cost.
Moreover, it is difficult to obtain an appropriate cutting surface by the influence of the seal layer 2 existing between two sheets of substrates in the case of cutting two sheets of substrates bonded together, differing from the case of cutting one sheet of substrate. FIG. 3 is a sectional view showing a method of cutting a substrate in a method of fabricating a conventional liquid crystal display substrate. As shown in FIG. 3, for example, as an instance of an appropriate cutting surface, in the case where the terminal surfaces of the first substrate 11 and the second substrate 12 and the terminal surface 2a of the seal layer 2 are formed to be flattened, the scribe crack 18 is provided at a position corresponding to an approximately vertical lower position of a terminal face 2a of the seal layer 2 in the first substrate 11. At this moment, when the first substrate 11 and the second substrate 12 are cut by the break bar 19, although cutting of the substrates is initiated from the scribe crack 18 as a starting point, the bias of stress in the vicinity of the terminal face 2a of the seal layer 2 occurs within the first substrate 11 and precision of cutting is lowered.
This is caused by the fact that symmetry of the stress as a center of the break bar 19 is out of balance since the seal layer 2 strongly restrains the first substrate 11. Therefore, it is necessary to add cutting precision and previously set the formation position of the scribe crack 18 and a striking position by the break bar 19 outward from the terminal face 2a of the seal layer 2. Therefore, there are problems that an area where the liquid crystal layer 20 in the liquid crystal display substrate 1 is formed becomes smaller and a display area in the liquid crystal display substrate 1 becomes smaller. It should be noted that said term “outward” refers to a direction of outside as a boundary line of a seal agent in the liquid crystal display substrate 1, accordingly, the term “inward” of the seal agent refers to within the liquid crystal injection area, that is to say, within the liquid crystal layer 20.
Moreover, in Japanese Patent Application Laid Open Publication No. 5-188387, a structure of a substrate forming a dummy seal layer made opposed to the opening portion of the seal area on the extra length portion in the vicinity of the external terminal of the substrate (electrode substrate) and its method of fabricating the substrate have been disclosed. This structure will be described below with reference to FIG. 4.
FIG. 4 is a sectional view showing a constitution of a substrate having a dummy seal layer disclosed in Japanese Patent Application Laid Open Publication No. 5-188387. As shown in FIG. 4, in the case where the dummy seal layer 21 is provided outward from the scribe crack 18, the stress applied to the first substrate 11 can be made symmetry to the break bar 19 in the mechanical cutting process. However, in this case, since it must sufficiently secure the extra length portion, there is a problem of reducing the display area in the liquid crystal display substrate.
In addition, even in the case where cutting of a substrate is performed by a laser (hereinafter, referred to as laser cutting) in order to prevent cutting surface from being roughed as seen in the mechanical cutting, although occurrence of cullet and particles can be suppressed, cutting face of the substrate is formed in a cracked shape just like peeled off by the seal layer being intervening between the substrates.
FIG. 5A is a sectional view showing a method of fabricating a liquid crystal display substrate by a conventional laser cutting and FIG. 5B is its perspective view. Concretely, as shown in FIG. 5A, on a surface of the superimposed substrate 13, which is made by the first substrate 11 and the second substrate 12 sandwiching the seal layer 2, the scribe crack 18 is formed, in the case where laser cutting is performed to the substrate on which the scribe crack 18 is formed by irradiation of a laser 26 from a laser head 25, since the seal layer 2 strongly restrains the first substrate 11 and the second substrate 12, symmetry of stress is out of balance, thermal stress by laser irradiation acts asymmetrically to the scribe crack 18, and cutting of the substrates 11 and 12, and the seal layer 2 linearly can not be carried out. As a result, as shown in FIG. 5B, the cross sections of the first substrate 11 and the second substrate 12 are formed in a bend shape in the position where the seal layer 2 is formed. Particularly, since the cross section of the second substrate 12 is formed in an expanded shape toward the extra length portion 3 or the terminal portion 31 on the first substrate 11, there is a problem that lowering the cutting precision is occurred.
Furthermore, in a conventional method of fabricating a liquid crystal display substrate, after a liquid crystal agent is injected into the liquid crystal display substrate 1, there is a problem that a process (panel washing process) in which the liquid crystal agent attached on the liquid crystal display substrate is washed by a panel washing device using a washing agent and pure water is multiplied. The panel washing process concretely refers to a process in which a plurality of liquid crystal display substrates are stored in a specialized cassette, immersed in a tank and washed. Because a washing agent employed in this washing process contains the component corroding metal, it may be possible to occur an incomplete conductivity of an electrode and the like formed on the terminal portion by residual of the washing agent on the liquid crystal display substrate. This is caused by the fact that the terminal face 2a of the seal layer 2 forms a concave portion to the terminal faces 11a and 12a of the first substrate 11 and the second substrate 12, and a liquid crystal agent, a washing agent or the like remains in this concave portion.
Therefore, there are problems that facilities using in the following processes of the liquid crystal display substrate are likely to be polluted by having such a structure, the extra cost is occurred and the yield is lowered as well as the washing process has to be provided over and over again in fabricating a liquid crystal display substrate.